Medical interventions on the heart of a patient are frequently performed with the aid of a catheter. To assist the doctor in the introduction of a catheter, the intervention is regularly performed in the environment of an X-ray recording system, e.g. the patient lies on a bed in an C-arm X-ray system. This enables 2D X-ray projection images to be recorded during the intervention. During this, the doctor selects the so-called projection angle, i.e. the settings of the C-arm X-ray, suitably to enable him to see a catheter as optimally as possible.
To assist the doctor, also known is the provision of images of the heart which were taken before the intervention. It is precisely with imaging of the heart that is has been found to be a problem that the heart is subject to continuous movement. In this regard, it has been found to be advantageous if, during the recording of the images generated for the generation of the 3D X-ray image data set, an electrocardiogram is recorded so that a phase in the electrocardiogram can be assigned to each image. To be more precise, a cyclically repeated curve in the electrocardiogram is divided into a plurality of intervals each defining a phase. The image data is then sorted according to the phases with a 3D image data set being generated for each phase. More details on this may be found in the patent DE 10 2004 048 209 B3.
Also known are methods for motion correction when imaging the beating heart. In such methods, the images recorded for the generation of the 3D X-ray image data set are assigned calculated motion information relating to a previously selected reference heart beat phase. During the reconstruction of the 3D X-ray image data set from these two-dimensional images, the motion relative to the selected reference state is mathematically corrected in a suitable way so that a high-quality image of the heart for the selected reference phase is obtained. More details on this may be found in patent applications US 2004/0136490 A1 and US 2006/0133564 A1. The U.S. Pat. No. 5,287,276 discloses a comparable method which is used to correct the respiratory movement of the thorax determined by means of a sensor during the recording of the images required for the generation of a 3D X-ray image data set.
During the image recording, the heartbeat phase can be used to trigger the recording of the images so that the 3D X-ray image data set for a selected reference phase is of particularly high quality, while other phases tend to be ignored.
Therefore the outcome of the methods claimed in the prior art is that a 3D X-ray image data set of the heart is provided which is assigned to a reference phase in the electrocardiogram of the heart. However, during the intervention, it may be the case that the 2D projection images recorded are not assigned to this reference phase. It is possible that this doctor performing the treatment does not even want this. In this case, it would not be advantageous to generate pictures from the 3D X-ray image data set assigned to the reference phase, which are, for example, superimposed on the 2D X-ray projection images which are assigned to another phase in the electrocardiogram of the heart.